text:
Do thermals stop rising when clouds are formed?
Glider pilots know that one indication of thermal lift is the formation of cumulus-type clouds.
My question is: Does the rising air (that lifted the moisture to form the the cloud) stop rising after the water vapor condenses?  Is there rising air above a cumulus cloud, or does the condensation somehow stop the upward movement of the air?

No, the opposite is in fact true. When the water condenses, it releases latent thermal energy, causing the air to rise even faster. That is why some glider pilots (who are appropriately licensed) fly, not just under, but into cumulus clouds to gain height.
When water vaporizes, it absorbs thermal energy. That is why, for example, humans sweat to cool down. As the sweat vaporizes, it removes thermal energy (heat) from the body. This thermal energy is stored in the water vapor, and will be released when it condenses.
The air in a thermal will only stop rising once it reaches the temperature of  the surrounding air, which can happen at different altitudes, depending on the state of the atmosphere. The main reason rising air cools down is because there is a relation between temperature and pressure. As the air rises higher, the pressure drops, and the temperature does the same. This can be depicted on a diagram of the temperature gradient, like this:

The thick red line is the ambient temperature of air at different levels. The oblique lines indicate the rate at which a column of rising air will cool down as it rises. As long as the thick red line is more inclined than the oblique lines, it is an indication that air will continue to rise, since it will not cool down fast enough to reach the temperature of the surrounding air.

May be worth noting that often the top of the cumulus cloud marks the end of the lift.

I'm not sure I understand what is meant by "thermal energy is stored in the water vapor and will be released when it condensates".  Does this mean that the air cools as moisture condenses out?  Why would this cause the air to rise faster?

Your third paragraph should read "The air in a thermal will only stop rising once it reaches the density of the surrounding air".  This is a significant difference because water vapour is significantly lighter than air (by a ration of 18:25.6).  So moist air will rise, even if it is the same temperature.

No.  You might notice flat bases on some of those clouds.  That flat base is the point at which the temperature and dew point spread reaches zero.  When the Temp/DP spread hits zero, visible moisture forms. The air is still rising, the only difference is that you can see it in the form of visible moisture (aka "a cloud").
If you were able to put on magic glasses that would make rising columns of air look like clouds from the very beginning of a thermal, you'd see the bases of the clouds start MUCH lower than what you can see normally.
We actually use those rising clouds as indicators of where thermals reside.  I have come very close to experiencing "cloud suck" in a glider and it is not fun.

That really would... Ok, that pun is way too obvious :)

...blow?  I agree.

A thermal does not continue upwards beyond the top of any cloud it might form, but it actually becomes stronger when a cloud does form, and can rise to the tropopause, creating towering thunderheads and many other weather phenomena.
As the air in a thermal rises, it expands, maintaining the same pressure as the surrounding atmosphere (which decreases with altitude).
this expansion against the pressure of the surrounding atmosphere does work, just as a gas expanding against a piston in a cylinder does work. The energy for this comes from the thermal energy of the air in the thermal, causing it to cool down.
Because a thermal is large and air is a poor conductor of heat, this occurs with only an insignificant flow of heat between the thermal and the surrounding air (and the mixing at the boundary is similarly small in relation to the mass of the thermal). Consequently, the change in temperature of a thermal with change in altitude can be calculated on the assumption that it is entirely due to the work done by expansion, and, for dry air, that turns out to be 9.8 degrees C per 1000 meters. This is known as the dry adiabatic lapse rate ('adiabatic' referring to physical processes that occur without heat or matter flow.)
As the rising dry air cools, it does not lose any moisture, so its relative humidity increases. When that reaches 100%, the air has become saturated, and further cooling will cause some of the moisture to condense, leading to the formation of a cloud. The moisture does not all condense at once; the amount that condenses is the excess over 100% humidity at the new, lower, temperature.
The condensation of this moisture releases the latent heat of condensation of this moisture, which compensates for some of the heat loss due to the work being done by the expanding thermal. Consequently, the lapse rate (rate of cooling with altitude) decreases within the cloud. The contribution of this condensation is dependent on the temperature (there is not much moisture to condense in cold air, even when saturated), but Wikipedia gives 5 degrees C / 1000 meters as a typical figure for the moist adiabatic lapse rate. Note that this is approximately half the dry lapse rate.
A thermal will continue to rise so long as it is warmer than the surrounding air (though there may also be an effect from the lower density of water vapor if the humidity of the thermal and surrounding air are significantly different.) Let's consider a dry/clear thermal in dry/clear air: as the thermal starts off only slightly warmer than the surrounding air and cools at the dry adiabatic lapse rate, this means that for it to rise to any significant height, the surrounding air must have a lapse rate (rate of cooling with altitude) very close to the dry adiabatic lapse rate (it cannot be higher, because that would be unstable: convection would spontaneously form and continue until this turning-over and mixing of the atmosphere reduces the lapse rate to the adiabatic.) (For completeness, I will just note that very close to the ground, the lapse rate can be super-adiabatic.)
A sufficiently-deep inversion layer (one where the air temperature increases with altitude), or one simply with a lapse rate below the dry adiabatic, will cause a thermal to stop rising (if it has not begun to condense) and no cloud will form. If, however, the thermal reaches the condensation level, then a cloud will begin to form, and its lapse rate will decrease to the moist adiabatic lapse rate for its temperature. If the temperature of the surrounding air continues to fall with altitude at the dry adiabatic rate, then the temperature difference between the thermal and the surrounding air will actually increase with altitude. This increases the thermal's buoyancy, making its lift stronger - an effect well-known to glider pilots - and requiring a larger inversion (or layer with a lapse rate less than the moist adiabatic) to stop it.
This is the primary mechanism by which the condensation of moisture drives thunderstorms, hurricanes and other non-orographic rainfall. A summer's day may start with an inversion stopping convection at a few thousand meters, but as the day warms up and thermals carry the heat upwards, the inversion is eroded by heating from below. By afternoon, the thermals may break through the inversion, particularly if condensation begins. With condensation powering the convection, it may go all the way to the tropopause and spread out under the stratosphere (which is a giant inversion), producing the anvil-head cumulonimbus cloud of a pop-up thunderstorm.
If the atmosphere's lapse rate is between the dry and wet lapse rates, it is only conditionally stable: if a mass of this air is lifted to the point where condensation occurs, it will now have a lapse rate less than that of the surrounding air, and will continue to rise, driven by the condensation of its moisture. One way this initial uplift can be caused is by the cold outflow of a thunderstorm pushing along the ground. This is the mechanism by which a derecho can travel hundreds of miles through a conditionally-stable airmass.


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How can this kind of confusion about taxi instructions occur?
A few days ago, I (a student pilot on a solo) had landed on runway 9 for a full stop taxi back. The taxi instructions were "alpha to 27 remain on this frequency". I missed some words in between these instructions, but after responding "alpha to 27" there were no corrections, so I continued my taxi to 27. At this point I should have asked for clarification. A jet was landing and I was blocking the exit as I had taxied and was holding short of 27. ATC responded saying I was at the approach end of 27 and instructed me to do a 180 and taxi to runway 9 (they were very nice about it though).
I've been racking my brain trying to think what those missing words were. I can't imagine they'd have said departure end of 27 instead of just 9. This may be one of those moments I'll never figure out, but would anyone more experienced have any idea what might have happened?
Unfortunately the airport is not on LiveATC.net and my GoPro died from low battery so this is all from memory.

I guess it would help to see the runway and taxiway layout. Could you add the airport where this happened?

@Bianfable Oh sure! It was KBKV. Here's an overview of the airport layout: here and here

The controller should have been more clear. I assume you were on one of the An taxiways? The controller should have said something like Alpha to Alpha-Two, hold short 27, this frequency... If they screwed up and wanted you on A6, hold short 9, that's on them. Also, if you notice you missed part of a transmission, there's no shame in saying tower, N1256, repeat last.

Yeah, I was probably on alpha 4 at the time. I definitely regret not getting clarification. I had heard "alpha" and "27" and figured i got the jist of what he said, which is a bad habit to avoid for sure.

@Hrothgar They should have noticed you going in the wrong direction long before you reached 27, so that's on them too. Don't beat yourself up over this much, mistakes happen and we learn from them and move on, and from the sound of it, a lot of mistakes were on ATC's side.

Also keep in mind that the controller vocabulary is really not that big (a hundred words maybe?), and in no time pretty much everything they say will be familiar, and things that are not familiar will stick out like a sore thumb.

Why not give the tower a call?
Although it is now several days since it happened, you could still call the tower (by phone) and ask them to clarify what happened. Explain to them that you would like to learn from the situation so that it won't happen again in the future.
It's a great opportunity to learn about the tower operations and many towers are open to these kind of discussions. Remember, they may learn from the situation as well.
If you are lucky they invite you for a visit and perhaps they will use the tape recording and relisten to the taxi instructions together with you.

"Tower, this is ... , please say again."

What airport was this at?

@CarloFelicione It was Brooksville-Tampa Bay Regional Airport (KBKV)

@DeltaLima Hmm, that's a pretty good idea. Unfortunately I'm leaving on holiday, but if it ever happens again(or maybe when I'm back) I think that'd be a really interesting thing to try.

Or call them now, and explain them you will be back after you holidays. BTW, enjoy your holidays!

Most ATC controllers will try to avoid using the words “to” and “for” for obvious reasons. Especially in giving taxi instructions. This is not patently true in all cases for all controllers. But, it is so with my local Class D airport. You might have heard them wrong. Or, they might have been having a bad day. The dead giveaway was that you just landed with the winds favoring 09. And now, ATC was about to put you on the runway with a possible tailwind instead of turning you back towards your landing runway. Your “taxi-back” should be a big u-turn. As you have noted, you should have asked for clarification.
Also, pay attention to the radio exchanges going on with other aircraft. It will give you better situational awareness to know where other aircraft are or will soon be. This will help you avoid conflicts.
It’s also a good idea to review the airport taxi diagram before starting your descent to enter an approach or traffic pattern. Having the diagram out and ready will help you maintain positional awareness once you have been given your taxi clearance.
On the far end of the spectrum of possible speculation, that radio call might not have been meant for you. Since you could not or would not hear the total call, it might have been for an aircraft with the tail number NA227 or something similar. Unlikely, but possible.

As a non-flyer, the obvious reasons aren't that obvious to me. What are they?

@Prometheus - the use of the words “to” and “for” are to be avoided on the radio so that there isn’t a confusion with the words two (2) and four (4). This is a similar reason to why the number 9 is pronounced “niner”. That way it is not confused with the German word for no. There should also be no numbers spoken above the number niner (9). Ten (10) is one zero. Eleven is one one. The number 12500 is one two thousand, five hundred. All to avoid confusion and mistakes. This rule/recommendation is broken on a consistent basis, though.

Yeah, I and a few other aircraft had just landed on runway 9 and a jet behind me was also landing runway 9, so taking off runway 9 would have made sense. I think as a student pilot you have a tendency to take ATCs words(or what I thought were ATCs words) as gospel, but I think that'll go away as I gain experience. No harm in asking them to say again too!

I continue my series of "not actually an answer but I got to say this":
The most valuable lesson you can learn from this is not figuring out afterwards what was said, but getting into a habit of always asking "Say again..." when you miss even a slightest part of a transmission. Ron stated it in the comments: no shame in that, not even a bit.
Whenever you allow yourself to guess the missing parts, you put yourself, and probably others in danger. Requesting repetition, every now and then you'll catch the grumpy controller that'll bitch at you for not paying attention, but never mind them. You don't want extra holes in your Swiss cheese.

True. Better safe than sorry.

I (and 34 other people) don't think that this qualifies in the not actually an answer realm. That's exactly what crossed my mind while reading the question. (Excellent advice BTW)

I try to respect the Q&A nature of this site, but sometimes I see a spot for some safety propaganda and shamelessly use it

@Jpe61 It wouldn't take much re-wording to make this technically an answer. "This kind of confusion can occur when people don't ask for clarification after they miss words."

I think Dean covered that nicely in his answer, he was there first, don't want overlap with it.

Is there a protocol for saying back what you think they said and then they confirm or deny it?

A short answer, yes. You are supposed to read back most instructions ATC gives you. If you get it wrong, they'll correct you, if you get it right, in most cases no further com follows. If you miss (some of) the instructions, for brevity it is best just to say for example "Tower say again for XYZ". You can ask ATC to say again any part of transmission, but that'll be more complicated I think. Again, if you miss stuff, do not guess and readback. Just admit to yourself you need to hear it again and request say again. There are very good reasons for this.

There's a lot of psychology involved in this resiprocal com stuff, especially when you miss something. Don't know if there is a Q with A for the subject here already...

Thanks for the advice! Hopefully I'll get more confident in my radio calls as my experience goes up. I think his lack of a correction gave me false confidence in what I was doing, but it's better to have a, possibly, grumpy controller than putting others in danger, as you say. It's something I don't plan on repeating!

No worries mate, solo student flights tend to end up as a collection mistakes, it's all part of the learning process. The fact that you decided to ask for advice here is a good sign.

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Are NDBs and VORs dying as a navigational method?
I am new to aviation, so bear with me on this question:
I have read in multiple places that the VOR/NDB navigational aids are dying out to GPS. Is this true? Are more modern aircraft being built with glass, digital instrument readouts that capitalize on GPS services instead of the traditional vacuum tube ADF and VOR Indicators?

"traditional vacuum tube ADF and VOR Indicators"  Tubes?  Pretty sure there are no vacuum tubes in the indicators.  Tubes wouldn't do well in the vibration environment of an airplane.

Yes, without a shadow of a doubt. Many airports now publish GNSS (Generic term for all types of satellite navigation) approaches, completly negating the need for those aids even during complex, critical phases such as approach and landing and take off and departure.
Modern GNSS systems are capable of utilising synthetic VORs where even when doing something such as flying a particular radial, the aircraft actually uses it's GNSS data to do so.
And, if you needed outright evidence, how about this quote from the UK National Air Navigation provider (NATS):

Commercial aviation – which has always funded the upkeep of the VOR beacons – now almost exclusively relies on the use of satellite navigation (read last week’s post on EGNOS for an example), making the majority of beacons an expensive and unnecessary financial burden. As such by 2020 we will be reducing their number from 44 down to 19.

Source: https://nats.aero/blog/2015/05/has-gps-killed-off-the-vor/

I'd suppose it would help cut down on expensive infrastructure as well. Reduce the number of giant VHF radio structures and NDB antennae helps keep $$ low......

@Jon Absolutely, see my edit :)

The thing that terrifies me, is the satellites could become a prime target for an enemy/terrorist org. What would happen if all satellite-driven services died due to an attack? Are there alternative navigational methods in that worst-case scenario?

@Jon I think that'd be a good candidate for another question if it hasn't been asked already. Suffice to say, yes - if nothing else, most modern aircraft are equipped with Internal Navigation Systems allowing navigation with no outside help at all

Ok. There actually already is a question for that. ATC for controlled airspace, and at wost-case, an old-fashioned magnetic compass, aviation map, and pen. :)  Also VFR flight using literal landmarks.

@Jon If there is terrorist activity that is capable of knocking out enough navigation satellites to render GPS useless, the word "terrorist" has to get replaced with "well funded state actor."  Also, when a well funded state actor decides to take out navigation satellites, that's a great time to be on the ground, at a pub... or maybe a basement. Basements are nice safe places =)

@CortAmmon Never underestimate the power of screwups. In 2016, the Air Force accidentally broke the time signal of GPS for 12 hours when they triggered a bug decommissioning a satellite, then ran into another bug that prevented them from fixing it until the end of the day. Though it didn't affect navigation, it degraded landline, wireless and broadcast radio services.

But what about NDBs? Using a NDB gives you information about your bearing (with respect to the NDB). GNSS can give you only information about your position; not bearing.

@Curd What about them? If you know your absolute position, and the GPS device knows the absolute position of the other aids (NDB, VOR, Towns, Waypoints etc) the it can tell you anything you like - your relative bearing, your distance etc without ever having to "talk" to them. In other words, they don't even need to physically exist and you'd never know while your GNSS was functioning

@Dan: example: you want to know what angle is between your baseline and the direction to the NDB. Just knowing your position and the position of the NDB (or anything else) doesn't tell you anything about the direction you are looking.

@Dan: e.g. you could use a NDB as substitute for a compass (if you know about  where you are and the NDB is far away). You can't do that with just knowing your position.

@Curd I see what you're saying, but I think it's a bad example as NDB's themselves have already mostly been phased out in favour of VOR's, which give the same data as a GNSS system would. Radio Direction Finding has a lot of issues in real life, and it can't give you a real life bearing without user input or slaving to a Direction Indicator anyway.

Yes, it is true. This FAA page has more info.

The Very High Frequency Omni-directional Range (VOR) Minimum
Operational Network (MON) provides a conventional navigation backup
service in the event of a loss of Global Positioning System (GPS)
signal. The MON includes the minimum number of geographically situated
VORs in the contiguous United States (CONUS) necessary to provide
coverage at and above 5,000 feet above ground level. Additionally, the
MON supports International Oceanic Arrival Routes and mission critical
military use.

From the Federal Radionavigation Plan the Gerry references in the comments:
ILS

ILS is the standard precision approach system in the U.S. and abroad.
FAA operates more than 1,200 ILS systems of which approximately 150
are CAT II or CAT III systems. In addition, DoD operates approximately
160 ILS facilities in the U.S. Non-Federal sponsors operate fewer than
200 ILS facilities in the U.S.
As the GPS-based augmentation systems
(WAAS and GBAS) are integrated into the NAS, and user equipage and
acceptance grows, the number of CAT I ILSs may be reduced. FAA does
not anticipate phasing out any CAT II or III ILS systems.
The NAS includes more than 1,300 NDBs. Fewer than 300 are owned by the
Federal Government; the rest are non-Federal facilities owned
predominately by state, municipal, and airport authorities.

NDBs

FAA has begun decommissioning stand-alone NDBs as users equip with
GPS. NDBs used as compass locators, or as other required fixes for ILS
approaches (e.g., initial approach fix, missed approach holding),
where no equivalent ground-based means are available, may need to be
maintained until the underlying ILS is phased out. Some NDBs may also
need to be maintained to facilitate training and proficiency
requirements. Most NDBs that define low-frequency airways in Alaska or
serve international gateways and certain offshore areas like the Gulf
of Mexico will be retained.

For the rest of the story, read the Federal Radionavigation Plan.

@Gerry Interesting document. I’ll have to read it in detail later. One thing that I did not know is that GPS signals are used by spacecraft.

In the case of VORs, maybe as a primary means of navigation it is dying out, but I honestly do not see them being phased out completely within the next decade or so. Most ANSPs prefer keeping them as a secondary means of navigation given that GNSS still relies on GPS developed by the US military.
As for NDBs, I think I've seen only one or two that are still in existence, so yeah they're definitely out.

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Who has the authority between captain and first officer in emergencies?
Yes I know, Captain has authority over First Officer.
I was reading about Airblue Flight 202 and according to the investigation, First Officer said these words 40 seconds before crash:

Sir turn left, Pull Up Sir. Sir pull Up.

Although many sources have questioned the investigation and its subsequent report, because of several facts including how the captain with over 25,000 hours and an unblemished flight safety record could make such mistake when he is so much familiar with the terrain etc., my question isn't about that.
What I want to know is that in case of an emergency or a similar incident of an imminent crash (as mentioned above), can a captain order the First Officer not to touch anything, or ignores his warnings or simply not listen to him at all? What the First Officer has to do or can do?

Even if there were legal print somewhere that entitled the captain to order the FO to let him fly into terrain, surely being alive-but-facing-discipline would still be preferable to complying?

Authority in the cockpit, especially in emergency, is very important in a principle called Crew Resource Managment, or CRM. A number of incidents similar to your example led to the formulation of this concept to enhance the coordination between the crew. The idea is that all crew members should be working together as effectively as possible to solve the problems at hand.
In emergencies, the crew need to be able to communicate. This means that the first officer should be willing to question the Captain, like they did in your example. They should also be willing to take action if they feel it necessary. However, communicating this action is also important, as evidenced in the crash of Air France 447, where the pilots were commanding different inputs.
Neither of the pilots should be ordering the other to do anything unless absolutely necessary. They need to get the attention of the other pilot, state the problem, say why it's a problem, and suggest a solution to the problem. Then they need to agree on a plan of action, and be clear about who is in control.
In your example, the captain's negative attitude may have prevented the first officer from saying anything more.  A better response from the first officer would have been to say something more along the lines of, "Sir, we are flying towards high terrain, we are not flying high enough to clear it. We need to either climb over it or turn left to avoid it. Do you agree?" This makes it clear to the captain what problem the first officer sees, and is clear about how the first officer thinks they should respond. It also includes a direct question for the captain to answer. Both pilots should be ready to communicate like this if necessary, and should also be making sure that they aren't creating an environment where the other pilot isn't comfortable with doing so. If the first officer still got no response, he should have been willing to take control, and should communicate to the captain that he is doing so, including the previously stated information about what actions he intends to take.

So in this situation it might be appropriate for the first officer to take the controls and pull up, but they'd say something about it? ("my aircraft")

@raptortech97 The key is communication. Either the first officer should tell the captain what to do (like he did) or he should do it himself. But they need to communicate with each other so they are both in agreement about the situation, and it's clear who is in control.

It's entirely reasonable for the First Officer to take control if he or she seems it necessary. Especially if the captain isn't responding to prompts for corrective action.
There are techniques you can use, in this example the FO called the captain 'sir'. If you normally address them by they're first name you could try 'sir' or 'captain'. You could recommend the take a turn or climb with increasing assertiveness.
If they fail to respond. You state 'I have control...' And tell them why. If they're not responding to prompts it's unlikely they'll be any resistance, they've probably lost situational awareness.

Adding this to other's answers, the First Officer (FO) is also a member of the crew. He or she, is therefore, also responsible for ensuring the safety of the aircraft to the best of his / her ability.
The FO has a control column and primary display identical to the Captain's. In a situation like this, it is essential for the FO to override the decision of the Captain. I can't say for all airlines, but I know certain airlines do practice the following scenarios in CRM trainings:

Pilot incapacitation
Pilot disorientation
A senior crew member performing incorrectly which compromises the safety of the aircraft

The GIST here is that the PF (pilot flying) may or may not recognize something is wrong. The PM (pilot monitoring) has to, using his experience as a superior pilot judgment,

Voice out his concerns
Suggest corrective actions
take over control when deemed necessary

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text:
Are there international standards to Air Traffic Control procedures similar to US standands?
In regards to air traffic control, FAA Order 7110.65 is the standard for policy and procedure in the USA. Do other countries use this also?
Is there an 'international standard' for air traffic control? If so, are there any notable differences between that and the service provided by U.S. FAA?

The way the question is rephrased is an improvement, but it is still too broad. You can't simply divide the world into the US and the rest. ICAO has 191 member states, each has their own particular differences from the ICAO SARPs (Standards and Recommended Practices). Maybe we can try an find out how the US procedures differ from the ICAO ones. But keep in mind that other countries deviate from the ICAO SARPS as well.

The answer to how it is worded now would be that the base principles are the same, but different countries have different quirks (such as the US using "cleared to land number 3" but not "behind the inbound 737 line up and wait behind). There's scope for someone to explain the Chinese airspace system and that they use metres for altitude instead of feet, etc. It's still a wide question but it could be at least somewhat answered as is.

Every country in the world generally operates from their own manuals. The International Civil Aviation Organization, ICAO, also has a standard that it recommends, and many countries have copied. From what I've been told, back when ICAO started up, they basically copied for their manuals, what the FAA had and used at the time. Over the years, the two have diverged in their designs.
There is no official/major standard, but most countries hold towards the ICAO recommendations, at least in general form. ATC's main purpose is the safe, orderly and expeditious movement of aircraft.

The FAA and EUROCONTROL jointly published a document in 2013 that provides a comparison of air traffic management starting in section 2.
Most differences have to do with the fact that the EU is comprised of multiple countries, while in the US, the FAA has full authority.
Organization:

The US system is operated by one single service provider using the same tools and equipment, communication processes and a common set of rules and procedures ... [while] the European system is much more fragmented and ANSPs are still largely organised by State boundaries.

Route/airspace management (including special use airspace):

[T]he Federal Aviation Administration (FAA) is responsible for airspace management and route design[;] in the amalgamated European ATM system, airspace design remains the prerogative of the individual States.

Direct link

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text:
What is the difference between CAMO and CAME?
Could someone explain the difference between a Continuing Airworthiness Management Exposition CAME and a Continuing Airworthiness Management Organization CAMO?

I think this explains: http://www.bazl.admin.ch/experten/luftfahrzeuge/03277/index.html?lang=en. CAMO are organisations. CAME is a document (or filing?).

Airworthiness Management Camo

CAMO is the organisation and CAME is a "book" that need to write.
This "book" contain procedure to explain how you will work (how you communicate with aircraft customers, how you manage your docs, etc...).


text:
Do I need to descend towards the Minimum Descent Altitude if I have the airport in sight?
I have some questions about circle-to-land approaches.
If we have the runway in sight above MDA, do we need to continue to descend to MDA on downwind? Can we just keep fly like a traffic pattern until abeam aiming point and then start the descent?
Similarly, If during circle to land approach we lose the runway on downwind but we are above MDA, do we need go missed still toward to the runway? Since we are above MDA we should still have obstacle clearance....

Regarding your second question, we've sort-of covered this previously. Take a look at the answers here for more information on when you need to go missed during a circling approach. (We didn't specifically address what happens if you're above the MDA, but if you've already started the "circling" part and you lose the airport I'm pretty sure you have to fly the missed approach per the procedure)

No, you do not need to descend all of the way to the MDA if you have the required visibility to continue. In fact, I would recommend against it since it puts you awfully close to the ground while you are maneuvering to align with the runway.  Why do that if you don't have to?
MDA stands for Minimum Descent Altitude, and is just that.  The minimum.
As far as going missed, you would fly the missed approach in the same way because while you may have obstacle clearance where you are now, the missed approach procedure assumes that you fly it the correct way, and in this case you just have some extra padding since you started out higher.

Couldn't agree more. I've always suggested to students that they circle at the TPA, if possible, only descending to the MDA if it's necessary. Circling approaches are probably the riskiest "normal" IFR operations out there that most pilots will encounter.

I'd guess MDA for a circling approach would be pretty near pattern height, if there are no other obstacles around, but not below.

@rheitzman Actually, without obstacles the MDA is usually significantly below pattern altitude so that you can land even with low clouds.


text:
Where can I find real-time flight tracking with the least amount of delay?
I am an aviation fan, relatively new to the industry.  While I thoroughly enjoy plane spotting at my local KORD airport, at times I tune to LiveATC and Flightaware to get my fix.
Unfortunately, my observations are that flightaware is a bit delayed 3-5 minutes, and not all air traffic is shown.
I tried Flightradar24, it is more current, but wildly inaccurate at times and a bit "synthetic" as they try to fill in the data gaps.
Aside from getting into an actual ATC tower, which I am sure is nearly impossible for a civilian, what are my best options as far as getting my fix in?  Apps, services, etc (paid and free), doesn't matter.

If you have the opportunity of placing an antenna at your house with a good view on KORD and the surrounding airspace, FR24 might want to provide you with one of their receivers. They are looking to expand in that area.

Flightaware is also expanding their ADS-B network and has some hardware to provide to users willing to install it. (I suspect they're already well covered for KORD, though.)

As of April 6th 2016, flights in the US/Canada on FlightAware no longer have a 5 minute delay.

You can buy a DVB-TV USB stick for around €20, which will allow you to receive ADS-B data:

Up from that, you can get a high-end ADS-B receiver that costs about €750:

Finally, FlightRadar24 offers free hardware in selected locations:

Bear in mind that these devices will only allow you to receive signals within a relatively small area.
One thing worth noting is by contributing the data received by these devices, you get a free FlightRadar24 Premium subscription.
Lots more information is available at FlightRadar24 > Increase Coverage.

I don't know about where you are, but in the States, the only ones with ADS-B Out that I've seen so far are FedEx aircraft up at the flight levels.  They're hard to pick up visually from the ground.  This will change as ADS-B(O) becomes more commonplace.

@SteveV. I don't know where you have looked, but the vast majority of internationally operating airframes as well as the B737 and A320 family aircraft in the US have ADS-B Out (1090MHz).

A good pilot is always learning, apparently!

If you don't mind dropping some cash, a handheld radio scanner will let you listen to as-it-happens ATC transmissions.
Combine that with a current copy of the Chicago O'Hare approach procedures (near the bottom of the page) and you'll be able to follow traffic in real time by looking out your window.
However, if you're not tied to O'Hare or you just feel like getting out for a day, head over to Midway.  There's a Giordano's right off the approach end of the airport.  You can get you some pizza while looking out the window and watching Southwest Airlines squeeze 737s onto a 6,500 foot runway.

You can get scanners pretty cheaply if you look around (they get even cheaper if you don't mind doing your own soldering) - they're not going to be as pretty as the $100 models though :)

Think EBay for inexpensive scanners.

All data from the FAA is delayed by at least five minutes unless you can show an actual need for real-time data.  Additional information is provided in their agreement for accessing the data (below).
As others have pointed out, there is various hardware that can be used to see real-time data in a small local area, but it only shows aircraft that are properly equipped.
As far as going into a control tower, take a look at What is the security policy for getting into a Control Tower?

From the FAA ASDI Memorandum of Agreement:

As a result of the aviation-related attacks of September 11, 2001 in
  the United States, the FAA reviewed security risks related to the
  ASDI/NASSI feed and determined that only Subscribers that are Class
  One Users are authorized to receive the full near real time ASDI and
  NASSI data set (this includes Direct Subscribers with Class One
  Indirect Subscribers).  Subscribers that are Class Two Users are not
  authorized to receive near real time flight tracking and position
  messages.  Class Two Users are only authorized to receive the full
  ASDI and NASSI data set that has been time-delayed at least 5 minutes.
Class 1:
A Class One User is a professional aviation organization with an
  established flight dispatch or planning function that requires near
  real time positional flight-tracking capabilities.  This organization
  must have direct responsibility for dispatching or tracking aircraft
  it owns or be contracted by the owner of the aircraft to do so.
  Examples are airlines, regional air carriers, air taxis, any
  organization providing dispatch or tracking functions for aircraft
  owners, flight operation centers, government users (as described in
  Section
  5.5), and professional flight planning service providers.   Fixed Base Operators (FBOs), corporate flight departments, and part 135 operators
  must have direct responsibility for dispatching or tracking aircraft
  to qualify as a Class One User.  The FAA shall be the  final arbiter
  for any disputes regarding the interpretation of this Section.
Class 2:
A Class Two User is any user not meeting the criteria of a Class One User (e.g., most general aviation; non-aviation-related
  entities and individuals; any other entity without a specific
  requirement for near real time positional flight-tracking).  Class Two
  Users can obtain Class Two (time-delayed data) either directly from
  the FAA Traffic Flow Management System Hubsite Class Two ASDI/NASSI
  interface or from Direct Subscribers that provide time-delayed Class
  Two data.

Pinkfroot now has a series of apps available on the appstore, windows phone and android store.
The apps vary from satellite views to actually being able to point your camera at the plane and tells you exactly what plane it is and all the information about it.
You can check them out here:http://my.pinkfroot.com/
If your looking to just listen to atc you can get the app live atc or just go onto their free website and find you airport.
Check them out here:http://www.liveatc.net/


text:
How do I determine odd or even when working with altitudes?
I am always confused about how to calculate safety altitude, especially when it comes to even heights and odd heights, e.g. is 7500ft even or odd?

these is called the "hemispheric rule"

It would be very helpful if you would mention which country you're asking about; these rules can be different in different places

related: http://aviation.stackexchange.com/a/13210/1467

See below for the wording of 14CFR91.159 which is the reg you need to answer this question.  Note it says "Odd [or Even] thousand feet plus 500".  7000 is an odd thousand even though it is an even number.

§ 91.159 - VFR cruising altitude or flight level.
Except while holding in a holding pattern of 2 minutes or less, or while turning, each person operating an aircraft under VFR in level cruising flight more than 3,000 feet above the surface shall maintain the appropriate altitude or flight level prescribed below, unless otherwise authorized by >ATC:
(a) When operating below 18,000 feet MSL and—
(1) On a magnetic course of zero degrees through 179 degrees, any odd thousand foot MSL altitude 500 feet (such as 3,500, 5,500, or 7,500); or
(2) On a magnetic course of 180 degrees through 359 degrees, any even thousand foot MSL altitude 500 feet (such as 4,500, 6,500, or 8,500).

Do we know if the OP is in the US? Some countries have a north/south rule, not an east/west one.

Look at the thousands of feet only.
Is 7(thousand) even or odd?
I'm sure a mathematician views 7,500 as equally close to 8,000 as 7,000.
But in aviation terms, it is 7,000 plus another 500 feet, and therefore an odd altitude.

A mathematician would also see 7500 as an obviously even number

@raptortech97 This is why mathematician are not allowed to fly :P

Look at the first (most significant) digit. ahem, then 12000 feet is odd?

Sounds like that should be restated to be "Look at the number of thousands of feet to determine if even or odd."

@SentryRaven I hope that rule doesn't apply in the U.S. because my CFI is a math professor with a Ph.D in math. :)

This made me confused.

I don't find any of the other answers to provide a useful mnemonic, which is what you need for rote memorization of arbitrary rules like this. The one I learned (and still remember decades later) is this:
ONE = Odd for North and East
In other words, if you're on a North or East course (360 - 179), then use Odd thousands.
By elimination, if you're on a South or West course (180 - 359), then use Even thousands.

In the US there is a simple rhyme memory trick that you can use to figure out what altitudes would be valid for you to fly both VFR and IFR.
EAST IS LEAST - WEST IS BEST
What that means is that you fly odd number altitudes when flying East (Magnetic) and even number altitudes when flying in a magnetic Westbound direction.  For VFR just add 500 ft.
So valid West bound flights would be:  4000,6000,8000 IFR :  4500,6500,6500 VFR
Same with East Bound:  5000,7000,9000 IFR : 5500,7500,9500 VFR
A simple rhyme that works pretty well for me.   Also BTW, if you are filing then chose the initial leg as your filing altitude.  If you are under ATC control, you'll see that ATC will eventually ask you to climb or descend if your course leg changes your direction.   IF VFR, and you make a bend that takes you to the other side, then climb or descend even if you are not talking to ATC.  If talking to ATC, let them know.  They can either tell you to stay put or pilots discretion to the new altitude.
The reason for this is that head on's are pretty hard to do if everyone is flying the same direction.   You might get chewed up in the tail, but that's the job of the pilot in the plane overtaking you or ATC.

Welcome to the Aviation Stack Exchange! The rhyme you mention is great for converting true to magnetic headings, but why does "least" mean "odd"?

I remember it from my first flying days about 28 years ago when my flight instructor explained both magnetic correction and well as flying directions.  He said there were many mnemonics to remember but remember that it also applies to correcting magnetic headings +/- as well then you would only have to remember one of them.  As a beginning student pilot he knew that too much information could overload a newbie and get you confused.

“Least” is 5 letters, so it’s odd. “Best” is 4 letters, so it’s even.

@Kolom comment: Finally! I've started to think I'm the only one poor soul studying IFR rules and consistently confusing when to use odd and when even. No CFI (CRI) around me was kind enough to spell any useful mnemonic or at least any useful reasoning (even some foolish/childish/obscene one) helping to recall the rule correctly each time after couple of weeks of yet another futile attempt of memorizing it. I've never had such challenge even during my fights with PPL exams but this rule somehow got outstanding in its complete and illogical inexplicability.

@VanJone Yeah this is frustrating at times, but after you ingrained it in your brain, you just forget how stupid it is when you first hear it. And you become a proponent. It's even funnier how we do it in my native language; the word "east" starts with D, and the word "west" starts with B. D has one hole, B has two holes, and that's your odd and even. :)

I just remember that East is Odd, because East is Even woud make too much sense.
Like Nav lights - Red on the the left, because Red on the Right would make too much sense.

Red on the right would require rewriting the right of way rules.

NEodd, SWeven, North to East “odd” altitude plus 500.
SWeven, South to West “even” altitude plus 500.
East is least and West is best is for magnetic variation when figuring true course ves magnetic course.

Hi and welcome to ASE, what country/countries does this apply to? And what about sectors E-S and W-N?

Your answer is very jumbled...

AFAIK, different countries aligned along N-S axis use different odd / even assignments, it seems your examples relate to New Zealand, don't they? E-W seems to be way more consistent assignment but finding a good mnemonic on it was rather challenging.

“East is Odd, West is Even Odder” is a pilots mnemonic to remember what altitudes to fly at under visual and instrument flight rules. First, east and west are defined by the magnetic headings of zero to 179 degrees (East) and 180-359 degrees (West.)


text:
What does QBD stand for?
I recently heard the term QBD which the Aviation Dictionary explains is the fuel endurance in terms of hours. If it is an acronym, what is its expansion? If not, what is it derived from?

@VivianjeetSinghSudan There is also a more polite way to let members know that their question could have been answered with a bit of Google-Fu. A "Welcome to Aviation.SE" as the start of your comment especially with new users can make the difference. ;)

Welcome to Aviation.SE, topher! :)

@VivianjeetSinghSudan I did and found the explanation as in the question but no information on its origins. Google is subjective.

We don't direct people to Google; Google directs people to us.

I smell pride, @MarcksThomas

It comes from Q codes for morse communication. They where set up without a clear rhyme or reason that I can see besides being ordered alphabetically.

I'm not sure you can even say they are grouped alphabetically. QRJ? ("How many words have you to send?") doesn't have much in common with QRM? ("Are you being interfered with?"), just to mention one example.


text:
Can an IFR clearance be issued and flown through IMC in class G airspace?
Let's say an IFR flight was planned to depart from a non-towered airport with class G airspace extending from the surface to 700 feet AGL. The flight visibility and ceiling both go down to 0. Can the pilot get an IFR clearance?
If the airport had class E airspace from the surface up it would be in controlled airspace from the ground and I'm positive that an IFR clearance could be issued allowing IFR flight in that class E airspace right from takeoff.
In the case of class G airspace from the ground, the airspace is uncontrolled. Could an IFR clearance be issued that allows IFR flight and waives the basic VFR weather minimums for class G airspace?

Related -- see all answers -- https://aviation.stackexchange.com/questions/47569/can-i-go-into-clouds-if-i-got-ifr-clearance-uncontrolled-airport

The key point is in your last sentence:

In the case of class G airspace from the ground, the airspace is uncontrolled.

Uncontrolled airspace is, well, uncontrolled. An appropriately rated, current pilot, in an appropriately equipped aircraft, may fly IFR in class G airspace without either a clearance or a flight plan. There are no clearances to waive VFR minima in class G, because the flight is conducted under IFR.
If an entire flight is flown in class G airspace, a pilot does not need to talk to a controller at all. When class G airspace is overlaid by controlled airspace, like class E, the pilot will need a clearance before entering controlled airspace. The controller will provide a clearance (FAA Order  7110.65, p. 4-3-2):

WHEN ENTERING CONTROLLED AIRSPACE (instruction), FLY HEADING (degrees) UNTIL REACHING (altitude, point, or fix) BEFORE PROCEEDING ON COURSE.

Once the pilot is released for departure, they would depart IFR in class G, where they would be responsible for their own terrain and traffic clearance (using tools like an Obstacle Departure Procedure). As soon as they climb into class E airspace, they receive the benefits and responsibilities of flying in the ATC system.
An interesting border case is raised by wbeard52. In this case, a pilot departed a class G airport with class E starting at 700 AGL, and broke out of the clouds before entering controlled airspace. The ruling basically said that taking off in this situation without a clearance is not explicitly illegal, but falls under "careless or reckless operation" prohibited by FAR 91.13.

I heartily disagree that you can conduct an entire flight under IFR in class G airspace.  I know this is old, but as the accepted answer here it comes up as the second hit on a Google search of IFR in class G airspace.  I am disappointed that there is no commentary challenging this assertion.  So, I hearby challenge you to explain how conducting an entire flight under IMC in Class G airspace could be legally considered IFR vs a violation of VFR cloud clearance requirements.

P.S.  Your explanation should include a description of how one would maintain safe and appropriate separation from other IFR traffic in the Class G.

@MichaelHall Whatever is not prohibited is permitted. What regulation do you think would prohibit conducting an entire flight under IMC in Class G airspace? Note that 14 CFR § 91.173 prohibits IFR in controlled airspace without a clearance, but not in uncontrolled airspace.

@Terran Swett, I normally espouse a similar libertarian philosophy on these matters, but I stop at gross negligence that endangers others. To answer your question, the one that requires you to have 1 mile vis and remain clear of clouds in class G airspace, and the one cited above that prohibits careless and reckless operation. But, you flipped the question on me. I wasn’t asking about IMC, I was asking about IFR.

To further clarify the point I’m driving towards, let’s take weather completely out of the equation: It is VMC, CAVU, clear and a million, and you want to conduct a flight entirely in Class G airspace. If you wish to conduct it under instrument flight RULES, how would you actually execute this plan in accordance with the rules? Please be specific, and don’t mix IFR and IMC terminology.

Outside the US, uncontrolled enroute IFR in class G is common practice. For terrain avoidance, there are the Instrument Flight Rules. For traffic avoidance, you can either rely on the big sky / small airplane theory, which in sufficiently desolate areas is not very risky compared to e.g. the risk of engine failure, or use air-to-air frequencies to mutually deconflict without any ATC involvement (e.g. 126.7 MHz in Canada). These days we have ADS-B as well. This sort of practice is almost impossible to do safely and legally in the continental US.

Bonus given in recognition of certain points made in this answer, but not necessarily because I think it's the best possible answer.  (Naturally, I'm not allowed to give a bonus to my own answer :) )  Actually, I'd prefer to award the bonus to the QUESTION, but that's not possible either.

If a pilot calls for clearance from  an uncontrolled airport, as long as there is no conflicting traffic, the clearance is simply, "N1234 cleared from the XXX airport to the YYY airport as filed, climb and maintain 6,000, squawk 1234, clearance void...." It doesn't matter the weather at the airport. There doesn't need to be, "Upon entering controlled airspace..." You will receive IFR separation from all other IFR aircraft (including XXX arrivals who may have descended below controlled airspace).

Let's say an IFR flight was planned to depart from a non-towered airport with class G airspace extending from the surface to 700 feet AGL. The flight visibility and ceiling both go down to 0. Can the pilot get an IFR clearance?

Yes.  The ATC clearance will use the words "when entering controlled airspace"...

Is it legal to takeoff from a Class G airport with less than 1 sm visibility?

I don't know. Here is an interesting ALJ decision from one pilot who did that.  Although, his specifics are just a little different.  An excerpt from the decision.  Case 3935.

Respondent has appealed from the oral initial decision
  issued by Administrative Law Judge Joyce Capps at the close of an
  evidentiary hearing held in this matter on July 8, 1991. In
  that decision the law judge found that respondent's takeoff from
  an uncontrolled airport into clouds without a clearance or
  release from air traffic control (ATC) was not a violation of 14 C.F.R. 91.155(a), but was in violation of 14 C.F.R. 91.13(a).

It's important to note that the ATC clearance begins upon entry into controlled airspace and NOT before. No separation services are provided until then. Another thing to note is that class G airports typically don't have departure procedures, so terrain/obstacle impact is a very real threat.

The only exception I've found to "class G airports don't have departure procedures" is KTNX -- but unless you're doing "black" things for the USAF or are a Janet pilot, good luck flying into/out of there!

Wow! Great find on Case 3935. I found the FAA's response both amusing and true With regard to respondent's assertion that, "[i]f anytime an aircraft enters clouds in uncontrolled airspace it is careless without a clearance then the FAR's should be changed," we note that it would be neither wise nor possible for the FAA to attempt to specifically prohibit every form of conduct that it considered careless.

Many Class D airports revert to Class G when the tower is closed. They usually have obstacle departure procedures. and often SIDs, depending on the surrounding terrain and obstacles.

@UnrecognizedFallingObject --  Re "The only exception I've found to "class G airports don't have departure procedures" is KTNX" -- the first one I googled had departure procedures -- see https://flightaware.com/resources/airport/KCVO/procedures

@quietflyer -- you wind up hitting Class E at 700' AGL when taking off from KCVO.  in the KTNX case, there is no E airspace around it, as far as I know

@UnrecognizedFallingObject -- interesting, thanks.  PS didn't expect a quick reply as it seemed you hadn't posted a Q or A in quite a while; thanks all the same.

@UnrecognizedFallingObject -- note however that the published minimum for the Corvallis Two departure from 35 lists a 400' ceiling, so clearly it is envisioned that the aircraft might be in cloud before reaching Class E airspace.  Thanks for the clarification re KTNX all the same though.

@newmanth: Traffic separation services will be provided in a limited manner between the departure and other IFR traffic, in the form of a "block" around the airport for perhaps five nautical miles (one-in-one-out operations). Terrain separation services will not be provided until entering Class E airspace, and really not before reaching the MVA.

Most non-towered airports are Class G until 700 or 1200 AGL. There are MANY non-towered airports with IFR approaches and ODPs. Every time you descend while IMC into Class G on a published approach or depart on an ODP or Diverse Departure after being released for an IFR departure, you are legally flying in Class G while IMC.

There is a good point being made here that ties in the accepted answer, with the one Ian W just made above.  In the cases you describe the pilot would either be launching within an expected window of time whereby an IFR clearance would become active upon reaching controlled airspace, or entering uncontrolled airspace at the tail end of a published instrument approach procedure for which they are cleared.  If neither of these conditions are met, you are not IFR.

There is no doubt that the FAA envisions flight under Instrument Flight Rules in Class G airspace as something that may be done in compliance with the regulations.
For example, as another answer pointed out, page 4-3-2 of FAA Order JO 7110.65W gives an example of an IFR clearance containing the following language:

WHEN ENTERING CONTROLLED AIRSPACE (instruction), FLY HEADING (degrees)
  UNTIL REACHING (altitude, point, or fix) BEFORE PROCEEDING ON COURSE.

Also, as another answer noted,

Most non-towered airports are Class G until 700 or 1200 AGL. There are
  MANY non-towered airports with IFR approaches and ODPs. Every time you
  descend while IMC into Class G on a published approach or depart on an
  ODP or Diverse Departure after being released for an IFR departure,
  you are legally flying in Class G while IMC.

Here are examples of approach and departure procedures published for an airport in full-time Class G airspace (Class E airspace begins at 700' AGL in this location) -- https://flightaware.com/resources/airport/KCVO/procedures
Another answer mentions a 1993 NTSB ruling finding that a pilot who took off in uncontrolled airspace in IMC conditions with no IFR clearance at all was in violation of FAR 91.13.
Page 5 of the same ruling states the following:

According to FAA aviation safety inspector Lawrence Smith, the
  standard procedure for taking off from an uncontrolled airport in IMC
  is to seek an ATC time-limited clearance to depart from the airport
  and fly into controlled airspace according to a pre-filed flight plan.

(italicization and bolding added)
Therefore the answer to the actual original question

Let's say an IFR flight was planned to depart from a non-towered
  airport with class G airspace extending from the surface to 700 feet
  AGL. The flight visibility and ceiling both go down to 0. Can the
  pilot get an IFR clearance?

is unambiguously "yes", at least if the pilot is operating under part 91.  (For why this matters, see https://www.thinkaviation.net/standard-takeoff-minimums/ .)
If the original question were "Do the FAA and NTSB look favorably on flights conducted in IMC conditions in Class G airspace with no associated IFR clearance of any kind?", then the answer would have to be "no".
It does seem unfortunate that this latter point is not explicitly spelled out in the regulations.  Likewise the issue of what actually is the distinguishing characteristic of a flight that is operating under "Instrument Flight Rules"-- is it simply the fact that an IFR clearance has been issued in association with the flight, or is it something else?  These are apparently matters that have somehow "slipped through the cracks", just like the issue of clearly stating whether various regulations prohibiting certain activities in Class-E-to-surface airspace surrounding an airport also pertain to the airspace enclosed by a Class-E-to-surface "extension".  (For example see Does FAR 91.155c apply to class E surface extensions? )

Related-- see all answers -- https://aviation.stackexchange.com/questions/47569/can-i-go-into-clouds-if-i-got-ifr-clearance-uncontrolled-airport

I want to make clear that the "when entering controlled airspace" phraseology only indicates that ATC has authority in Class E airspace only. HOWEVER, this does not mean your IFR clearance only becomes active upon entering Class E airspace. For traffic separation purposes we treat you as IFR from the moment we say "cleared to," and after issuing an IFR release (even from a Class G airport) we will not issue any other IFR release from, or approach clearance into, that airport. Of course some other yahoo may depart IFR without a clearance and remain in G airspace, which we can't prevent.

You ask: "Could an IFR clearance be issued that allows IFR flight and waives the basic VFR weather minimums for class G airspace?"
The answer to the first part of the question is an unequivocal YES. An IFR clearance that is effective within Class G airspace can be issued, and is in fact issued every single day across the NAS.
Whether that IFR clearance waives the basic Class G VFR weather minimums is a trickier conceptual problem. Since the receipt of an IFR clearance is not required to go below VFR weather minimums in Class G airspace, can it be said that having a clearance "waives" those minimums? As the other answers point out, probably not.
Having the IFR clearance means two things:

When you enter Class E airspace and you have not suddenly broken out into weather conditions that meet the basic VFR minimums for that airspace, you are not in violation of the FARs.
No one else in the vicinity of the airport will be operating on an IFR clearance, which provides a significant measure of safety as regards other air traffic.

Of course it is still possible that an aircraft could be operating under VFR in the vicinity of the airport, and they may even be operating under IFR despite not having a clearance—which is, strictly speaking, legal, although (as has been pointed out) it may be construed as "careless and reckless" depending on the particulars of the situation.

Suggested edit-- the answer would be clearer to me as follows, but use your own discretion -- "Since the receipt of an IFR clearance is not required to go below VFR weather minimums while operating under IFR in Class G airspace..."

If the flight is conducted entirely in class G airspace, then possibly.
Pilots operating an aircraft under Part 123 or Part 125 cannot do so as the it requires at least 1 NM visibility for an aircraft with 1-2 engines and at least 1/2 NM visibility for aircraft with more than two engines.  Flights conducted under Part 91 operations allow for a departure under zero-zero conditions, though it is not advisable to do so.
If one does conduct the flight under Part 91 operations in Class G airspace in zero-zero conditions, an instrument rated pilot may depart into these conditions without an IFR clearance (though the pilot may want to have his/her head examined if they tried this!).  It would not be permissible for any segment of this flight to enter controlled airspace in IMC without first filing a flight plan and obtaining an IFR clearance before entering.
On a side note, if you remained in hard IMC in class G airspace with all nearby airports in zero-zero conditions, you would not be able to land as I don't know of any such airports equipped with a CAT III-C ILS approach into it.
Departures into class G airspace with an Class E shelf overhead is commonplace.  However the pilot must file an IFR flight plan prior to contacting either the local flight service station or clearance delivery from a nearby towered airport.  Typically, the clearance will be issued with a clearance void time, meaning that the pilot must make the departure and make contact with an ARTCC befor that time or a new IFR clearance must be obtained.

I disagree with your very first statement, but otherwise an excellent answer. (See my other comments on the "accepted" answer...)

A late response.
Instrument Flight Rules require that the aircraft is under the control of a 'separation manager' usually ATC authorized to provide separation.  ATC are not authorized to provide control in Class G airspace, so there is no separation from other traffic. The aircraft captain is therefore required to separate and keep well clear from other traffic. This is done by applying the Visual Flight Rules and VFR can only be flown in Visual Meteorological Conditions (VMC). Therefore, taking off in weather that makes staying VMC impossible is not legal.  IFR cannot exist in Class G airspace.
In Class E airspace you can fly IFR and be required to maintain VFR separation from aircraft not flying IFR that the controller may not see.

The FAA responded to this question in 04/19/16 referencing a 1993 NTSB ruling: “91.173 requires an IFR flight plan and ATC clearance in ‘controlled airspace’ but is silent with respect to ‘uncontrolled airspace.’ Per this regulation and assuming an IFR capable aircraft and pilot, it would also be permissible to fly in IMC without a clearance. HOWEVER, 91.13 prohibits operating an aircraft in a careless or reckless manner, and the NTSB has previously ruled that under certain conditions, takeoff into clouds without a clearance or release was 'extremely dangerous' and in violation of 91.13(a).”

The key phrase is “...under certain conditions...”. So, flight from Class G in IMC is technically legal even though it is actually stupid and reckless. The NTSB has grounds to take legal action if they choose. It is a grey area.

By the way, welcome to AviationaStackExchange. feel free to Ask, Answer, and Comment on any topic. Just remember, unless you have something materially new or you can contradict the previously accepted posts with citations, to stick with answering active posts instead of dredging up ancient ones.

He is contradicting the accepted answer, and I agree with this one.  (I went in circles on another post regarding this issue.)  There are certain key elements required to operate under Instrument Flight Rules.  If you don't meet them you are not operating according to IFR, you are merely flying in IMC.  There is a difference.

@quiet flyer, I don't  know, I didn't say that.

@IanW -- where in the FARs does it spell out that an aircraft flying under Instrument Flight Rules in uncontrolled airspace must be under the control of a "separation manager", or something similar?

I just came across this thread searching IFR in Class G.  It seems that the answers here are missing the question, "Can an IFR clearance be issued and flown through IMC in class G airspace?"  This appears to be like asking if the roads from my house to the airport are icy, can an IFR clearance be obtained and driven on icy roads to the airport?  Obviously ATC has no authority to grant nor deny any kind of clearance to drive on an icy road.  Similarly, they have no authority pertaining to uncontrolled (class G) airspace.  The fact you have an IFR clearance upon reaching controlled airspace is irrelevant to how you get to the controlled airspace.  So the real question is (assuming class G goes up to 700 AGL), can I take off and climb to 700 feet AGL in IMC in class G?  The answer depends on whether a reasonable person would view that as reckless.  If it would be reckless, then the FARs prohibit it (91.13).

To reiterate what I've said in other comments, just because a clearance is not necessary to operate IFR in Class G does not mean an IFR clearance is impossible in Class G. An IFR departure who has been issued a release, and an IFR arrival who has been issued an approach clearance, "tie up" the airport; ATC will not issue approval for any other IFR operation once that release or clearance has been granted. The IFR clearance takes effect even though the aircraft is not in controlled airspace, at least from an ATC perspective.

Re --"So the real question is (assuming class G goes up to 700 AGL), can I take off and climb to 700 feet AGL in IMC in class G?" -- do you specifically mean without any IFR clearance being issued for the flight?  A)  If so, you should add this content to your answer.  B)  If not, how do you explain the fact that aircraft are flying under IFR in IMC in Class G airspace on a literally daily basis (granted, nearly always with some sort of IFR clearance being associated with the flight)-- see related answer https://aviation.stackexchange.com/a/92543/34686 for more.

Interesting situation to fly IFR in class G.  Class G has min VFR vis at 1 mi day.  Less than 3 mi vis is classified IFR so to me it appears you are IFR even when flying VFR in class G.

Do you have any sources to back up your answer?

There is a distinction between IFR and IMC. IFR means flying under instrument flight rules. IMC means Instrument Meteorological Conditions. Likewise VFR and VMC. You are only IFR if you have a clearance from ATC. As mentioned in the answers, departing in IMC without an IFR clearance is probably illegal and is definitely careless and reckless. Departing Class G in VFR conditions in the day means visibility of 1 mile and COC—3 mile is is clearly not IFR.

IFR conditions are classified as vis 1-3 mi and/or ceilings <1000 ft.  LIFR is vis < 1 mi.  This is an interesting subject and I have never seen anyone answer it to my liking even FAA ops inspectors. So to fly in class G at anything lower that 3 mi vis you are "flying VFR" in IFR conditions.  IFR vis regulations do not change for class G or any other class airspace.

I suggest you check up on what is or isn't IFR.  Here is a start. https://www.aviationweather.gov/taf/help?page=plot    Like it or not IFR conditions have always been 1<3mi vis.  In class G <1200 ft FAA allows an exception to fly VFR COC in IFR conditions (was beneficial for ag spray) but by that variance it does not change the fact that 1<3 mi is classified IFR weather conditions.  So my friend it is a paradox as I pointed out in the discussion.

Re "IFR conditions are classified as vis 1-3 mi and/or ceilings <1000 ft."-- that's just a label. It has no controlling regulatory power in Class G airspace. In Class G airspace, if you have one mile visibility and can stay clear of the clouds, you are good to go under Visual Flight Rules.


text:
Why are there no parachutes to carry the aeroplanes in case of serious accidents?
Sometimes I wonder why the manufacturers do not design a big parachute to carry the aeroplanes when serious accidents occur. Perhaps the high cost is the reason?! But is it more expensive than a human life!?

See also: Why are commercial flights not equipped with parachutes?

See also: Why don't commercial jet aircraft have a break-apart, parachute escape system?

I think the question is about a gigantic parachute for the whole airplane, not just passengers, so it would be a duplicate to 11864, not 593. The answer Khalid is that the added weight would be significantly more costly and the parachute would never be used. I can only think of two (2) incidents in all of history in which it might have been used and in both cases the aircraft landed safely anyway.

Short answer: such systems would take more lives than they save. Remember, every dollar you add to the cost of air transportation means a few more people will travel by cars and thus a few more people will die in car accidents.


text:
What is the difference in performance between variable pitch prop and two fixed propellers for take-off and cruise speeds?
Push-pull configuration aircrafts usually feature identical engines and propellers working only in tandem for multiple reasons like higher speed, better climb rate, reliability, cost, ease of maintenance, etc.
It may sound unpractical for piston engines were saving fuel will not outweigh the downside of one engine being a dead weight but may be a good idea for lighter electric or a combo, where engines may also be optimized for different propellers.
Can it be possibly beneficial to have tractor prop for take-off:

blown lift
no FOD risk
less noise outside

and pusher specifically optimized for cruising:

larger diameter as no ground clearance issue
no parasite drag
more stability
less noise in cabin

Benefits to consider:

efficiency
higher achievable speed
higher altitude
still two motors for redundancy

Problems:
Stowing nose prop.
Foldable prop should be cheaper than VP.
Less take-off power.
Electric motor for tractor could drive 4-bladed prop at peak power.

What do you want to do with the set of props not optimized for the current flight speed? Let it windmill? Put it into a bay ? Keep it as a non optimised propeller still trying to power the aircraft? Let them acts as airbrakes? (Feathering seems to be excluded as you don't want pitch variability enabled)

whatever will be the optimal solution. Putting into a bay / folding would be probably the best one for low speed prop to minimize drag for a high speed one and windmill may work for a cruise prop as it is only for a short time period

To stow a propeller while continuing to use the engine you will need a clutch, which is usually a heavy and relatively complicated piece of equipment.

@aehere-supports-monica I'm considering two engines and props. Do you think it may be possible to have both propellers on the same engine with a clutch?

I would expect an engine to weight even more than a clutch, but yes, multiple loads on a single engine are not impossible.

The best option is a horizontally locked pusher propeller and winch launching. Landing will be in unpowered glide. No deadweight from second engine.

The Rutan Voyager aircraft had two different size engines and shut one down part way through the flight, but that aircraft had a massive fuel to structural weight ratio at take off, so the optimal cruise speed was reduced drastically during flight as fuel was consumed. The reason for shutdown was to keep the remaining piston engine within its best efficiency load range.

Tandem engines are rarely the same and the rear in every installation I know of (100s of designs) has less power, because it loses about 30% in efficiency from being in the front engine's wake, so it makes no sense to waste weight and fuel there on a full sized engine. In fact, there are few reasons for tandem engines as few of your reasons are true, aside from the engine-out issue on multi-engine aircraft, and not being able to find a powerful enough engine. You are vastly better off having a single engine - more efficient and also less likely to fail (2 engines = 2 X the odds of a failure).

The Voyager aircraft was a push-pull twin with different engines/props.
The front engine is a 130 hp air cooled 240 ci engine.
The rear engine is a 110 hp liquid cooled 200 ci engine.
Both engines turned Hartzell hydraulic constant speed props developed in just 17 days.
The front engine had excellent power-to-weight ratio, but was less efficient.  The rear engine was heavier, but was very efficient.
The plan was to operate both engines for takeoff and climb.  Then, at altitude, shut down the front engine and just operate off the rear for the duration of the around-the-world flight.
Towards the end of the flight, they had a venting / fuel starvation issue that caused the rear engine to shut down.  They restarted the front engine to keep them aloft until they could sort out the fuel delivery problem.
In general, you want variable pitch propellers when the aircraft needs to operate over a wide range of operating points (speed, altitude, and thrust level).  This is often simplified in general aviation to takeoff and cruise -- or climb and cruise -- but the operating envelope is more complex than that -- particularly for high altitude aircraft.

This doesn't specifically answer the question in the title, but from the body of your question I would say it's possible, if you had an electric push/pull configuration with a motor in the nose and one in the tail, or at the back of a fuselage pod with booms like a Cessna Skymaster.
The aft facing motor could use simple fixed pitch folding propeller that folds aft and trails in the slipstream when not being driven (popular with motor gliders) and it would be used only for take off and climb, with climb-optimized pitch.  In cruise that motor could be shut off and its batteries assigned to the front motor and its blades would fold into a near zero drag trail position.  The front motor could have a fixed pitch prop optimized for cruise.
The key issue would still be worst-case climb performance.  It would have to be able to make enough thrust on the single cruise pitched prop at the front to climb decently if the back motor failed.  Possibly if the front electric motor had some sort of emergency boost feature, where it's torque could be temporarily increased (enough to get its coarse pitched propeller up to red line) for a certain number of minutes without overheating, would be sufficient for single engine safety, with the rear propeller folding back on its own for you.
For single engine performance on the rear motor, you might get away with just a brake for the front propeller to stop it from windmilling if its motor failed.  Not as good as feathering, but far less drag than windmilling.


text:
Do rotorcraft flight hours count for airlines requirements?
I have a question about flight hours.
Many civil airlines require first-officers to have over 1500 hours.
I have 300 hours for fixed-wing, and also have 2000 hours for rotorcraft(helicopter).
In this situation, do I have over 1500 hours as necessary to apply?

the country of jurisdiction and/or the airline is probably a factor in this. could you tell us at least what country has issued your pilot's licence?

FAA Licnese! My questioning gist is that airlines requiring 1500 hours can be counted by my combination hours of 'FW hours + HC hours'

Please don't make more work for others by vandalizing your posts.  If you want to say thanks, upvote a comment or answer that helped solve your problem, but don't remove your question's content.

US Federal law (the Colgan Rule) requires both pilots to have an ATPL for flights under part 121. In most cases, an ATPL requires 1500 hours, but only 250 of those hours need to be in an airplane per FAR 61.159(a)(5).
Major airlines have substantially higher minimums than the FAA, and most won’t even look at you without 1000+ AMEL turbine PIC. The only common exception is for ex-military pilots.
In contrast, regional airlines are indeed hiring folks who meet the legal bare minimums—or are close enough they’ll cross the line during training.  They were happy hiring first officers at 250 hours (the ICAO minimum) until the Colgan Rule was adopted, and they’ve never recovered from the disruption it caused in their hiring pipelines. While the common joke about “1500 and a pulse” isn’t quite true, it’s not entirely wrong either.

There is no single answer across the board that helicopter  time will "always" or "never" count for airline hiring; each airline will specify if they consider helo hours or not.
Major airlines that I'm aware of typically specify their minimums in terms of fixed-wing hours only, although regional airlines may be more receptive to helo time.


text:
Do pilots pilots keep track of their groundspeed, by head?
For VFR nav. flights, do pilots have to keep track of their groundspeed, by head (done so by considering wind speed, wind direction, crosswind, tailwind etc.)?
And the purpose of this, is to check that you are on par with your pre-planned flying time?

Not really, usually we just keep track of time at waypoints and calculate the average groundspeed between segments, provided you aren't using a GPS with that capability.

Not really possible to give a definitive answer.  Depends on personality/flying style (some people like electronic aides, and even use them in their cars), what you're flying, how familiar you are with the route, and probably a bunch of other factors.

That depends on what you have in the cockpit, most planes these days fly with some kind of GPS be it a full blown panel mounted IFR certified unit or just an iPhone app. All of the ones I have encountered either by default or with minimal effort will display your ground speed for you and there is really no need to manually compute it.
The main purpose of ground speed is to ensure that you actually arrive at your destination with more than vapors in your tank. Let's say you need to travel 100 nautical miles in a Cherokee. You have 1.5 hours of fuel on board which is legal for a VFR flight. You unexpectedly hit a 55 Kt headwind at altitude. You trip is now going to take you a little over 2 hours assuming you cruise out at 100 Kts/Hour. Knowing your ground speed ensures you have the information you need to know that you will need to land ~50 miles into the flight and gas up.
When flying IFR its also important so that you can provide ATC an appropriate time deviation if you are not going to make a way point when expected.
On a similar note, most decent flying apps will do fuel computations en route for you as long as you provide a performance profile.


text:
Do VOR's follow true north on a chart?
Although VOR stations follow magnetic north, do VOR's on a chart follow true north?

Which charts are you asking about?

They are set to magnetic north, but magnetic north at the time they were instituted.  So if a VOR was buit in 1968, it would point at the location at which magnetic north existed in 1968, and if one was built today, it would point at the current magnetic north (5 year model).  The VOR's orientations aren't updated over time.

Aeronautical charts

@Pondlife. When I asked this question I was talking about Aeronautical charts that are, for example, 1:500 000. But I would like to know about 2 types of charts; aeronautical charts and plotting charts (where only radio stations, isogonal lines and lines of longitude and latitude appear). So finally, my question is, which orientation do VOR's follow on aeronautical charts and plotting charts? Any help would be appreciated.

@RyanMortensen - according to the FAA, if the charted North of the VOR and the actual magnetic North are off at least 6°, the FAA will have all of the aeronautical charts updated.

@Lungelo - The FAA aeronautical sectional charts have a scale of 1:500,000. The hi and lo altitude enroute charts for IFR flight vary in scale based on location depicted. Each set of charts produced by the FAA follows their update convention. There are also Plotting charts from Jeppesen that depict oceanic and coastal areas.

As per the FAA's legend they are referenced to magnetic north

Compass rosette will be based on the five year epoch magnetic
  variation model.

Both the signal and the representation on the sectional chart of a VOR will be oriented to magnetic North. There will be some fluctuation caused by magnetic drift. Adjustments will be made for this.
According to the FAA FAQ website...

Why is there a difference between the magnetic variation for the airport and the VOR located at the same airport?
  When a navaid is first constructed, the antenna is physically oriented
  to True North. Then a potentiometer adjustment is made to slave the
  navaid with Magnetic North. This action matches the isogonic line
  making it agree with a magnetic compass. Initially these two values
  are the same, but the magnetic variation of the earth changes at
  differing rates depending upon location and time.
Navigational aids go into service and remain online 24 hours a day,
  365 days a year. The FAA performs periodic maintenance; however,
  readjustments to match the isogonic value require a total shut down of
  the equipment, plus recertification and flight check verification.
  This process begins when a navigational aid is out of tolerance by at
  least +/-6 degrees. GPS databases use a MAGVAR model to calculate the
  most up-to-date magnetic variation.

one of the comments says the VOR headings are not updated as magnetic north drifts--??

@quietflyer - The FAA website states that the VOR headings are updated after they reach a certain tolerance.


text:
What are the handling effects of converting a dihedral wing to polyhedral?
I'm looking at plans to build a radio controlled (RC) glider that is launched by rocket boost mainly as a park flyer. I've been given a set of plans for a model that is a dihedral wing (see attached photo), and I am thinking converting it to a polyhedral wing, as I read that polyhedral wings are more stable for people new to flying as I am.
The new wing shape (I haven't drawn it out yet), would have a flat section over the fuselage acting as a partial cover for the rc components, then a 6 degree angle from there to mid point of the wing, and then another 6 degree angle to the tip.
Wing length and total angles/measurements would be the same, as would the airfoil (Which can be seen in the rib segments on the plan). My other option is simply adding the central flat fuselage cover section, and leaving the rest of the wing as is. (One note, the reason for the thinning of the rib sections in the front is that it is a partially built wing, there is a balsa skin over those parts, then the entire wing is coated in a lightweight monokote type material).
Is there any value in making this change to a polyhedral wing, or is it mostly a wasted effort that I shouldn't worry about doing?
Wing section (I have full plans if other angles are desired):

Ever break in the wing requires reinforcements since the spars and sheeting are cut. This increases weight and complexity. Just build it as designed.

In terms of in-flight behavior, the biggest change between dihedral and polyhedral (or tip dihedral) with the same overall stability is more roll response for a given yaw input -- this occurs because yaw-induced roll is caused by the skid presenting the outside wing at a higher angle of attack than the inside, and this effect is both more pronounced, per area, with the sharper angle of a tip dihedral or polyhedral tip panel, and is applied further from the centerline, so has a longer lever arm.
I'd agree, however, with the advice in another answer, not to modify your first kit.  Build to plans and instructions.  If you want to compare, get the kit built and the model flying correctly, then either buy another kit or buy materials (make photocopies or scans of the ribs and tip plates) and build another wing -- then you can compare the in-flight behavior for yourself.

Yaw is movement around the vertical axis, so if I translate correctly, a poly wing will produce sharper turns and greater roll? So a simple dihedral wing is a "genter" handling characteristic?

@JohnP almost correct.  A poly wing will produce more roll than simple dihedral, other factors equal.  Higher bank, coupled with some elevator input, can produce sharper turns, but the more usual use case is to give usable levels of bank from a smaller rudder or less deflection.

so... net effect for a new flyer who will likelier have a heavy touch on the controls would be a "twitchier" handling model with a poly vs di.

Depends.  Poly and tip dihedral are used on trainers -- but with small rudders and low flight speed (because poly recovers to level very positively).  A twitch at rocket boost speed, and you're likely to rip the wings off.

Raising the wing tips higher may drastically affect the frontal center of drag, by raising it above the center of gravity.  Especially for a rocket aircraft this could be absolutely disasterous. Look at the X-15.  You want symmetry and plenty of stability.

@RobertDiGiovanni the tips would remain at the same height.

@ZeissIkon for most rocket boost, there is not really any adjustment during the (1-3 secondish) boost phase. And all control is usually in the tail section, there aren't too many rocket boost gliders that have ailerons in the wing. But I see what you are saying.

@JohnP you may have to trim a little elevator down (tail upforce) for the rocket boost to keep it from looping.  See how it glides first, then start with the smallest rocket motor (Estes 1/4A3), or a good hard throw from a hill.  After boost, reset to glide trim.  You may find relevant info in "discus throw launch style" gliders. You may find it flies great without modifications.  Good luck!

@RobertDiGiovanni - That's the plan, actually. Start with a "dart" type throw and see how the flight works. Then gradually work up to higher throws (discus launch) and work on just circling back to me, getting used to the RC aspect. Once that is decent, then work on low power launches. I'm also meeting with a local RC club at their next gathering to ask n00blet questions.:)

@JohnP Dihedral, and especially poly or tip dihedral, is sometimes called "nature's ailerons".  A little yaw is just like a lot of aileron input.  At very high speed, one twitch on the rudder (usually mapped to the right stick for rudder-elevator models without actual ailerons) and the roll forces generated may break the wing spar.

If you are "new to flying" please do not start out by making modifications to your kit.  Build it faithfully and to the letter as best you can.  Secondly, rocket power may be too much for now.  Take your model to a good hill and learn to glide it first.
Changing a dihedral to a polyhedral will only make your build more difficult.  Biggest issues will be control throws and setting the CG correctly, followed by crosswind performance, which could be seriously affected by modifications.  Stick with the plan.
It is highly recommended to find a "mentor" at a local R/C flying club, or even to join one.
This will save many crashes, which end hours of building in seconds.  Expect a few during the learning process.

Useful advice, and it answers the question embedded at the end, but it doesn't answer the title question.

@Michael Hall really too many to mention, and impossible to quantify without testing.  IMHO not a good idea for someone "new".

Maybe not a good idea for a new builder, (as you pointed out) but for a new flyer?  The OP stated "I read that polyhedral wings are more stable for people new to flying as I am."  While admitting to being new at flying, he might be very accomplished at fabrication.  In this case the added stability (if true) would be a definite plus, right?

@Michael Hall yes, as a glider, added stability would be a plus, as a rocket plane, no.  It is very important to have frontal drag, CG, and thrust going through the same point on a rocket (just look at the ones with out wings).  I would also worry about cross wind effects and frontal drag change doing these mods.  Raising Cdrag would negatively affect handling by increasing pitch up tendency, but could be an interesting substitute for tail downforce if done right.  But I would follow the plan first.

@RobertDiGiovanni - Realize that the rocket boost will be in the order of 1-3 seconds at a max load of 10 newtons. I realize that disaster takes less than a second (Believe me, I've had my share of spectacular launch failures on new design rockets), but the actual "rocket plane" segment is very short and almost exclusively for altitude. I anticipate around 4-700 feet on an average C/D engine.

@JohnP big difference between a C and a D (1/4 A probably made you laugh).  See DLG videos on net.


text:
What is this seaplane shown in this photo?
While searching I noticed a seaplane page and found a particular seaplane photo that I have never seen before. While the other images showing other seaplanes do have the name, the description of this seaplane image, however, does not show its name. I also couldn't even see the registration on its hull.
So, is this seaplane possibly manufactured by Cessna? If not, then does anybody know what the name is?

That's a DHC-2 Beaver on floats. The dead giveaway is the unique trapezoid window.


text:
What UK aircraft looks like an Islander but with twin fins?
Driving on the M40 recently just south of Banbury, England, I saw a distinctive smallish plane I'm trying to identify — probably military from the dull grey/green color.
It looked a lot like the Islander, but:

It had a tailplane and twin fins
The tail boom was narrower in proportion to the body, and more distinct from the body than the Islander's is (I think I'm misremembering or mis-saw that part — I was driving on the motorway, after all)
The body may well have been a bit bulkier (or that may have been an illusion caused by the narrowness of the tail boom)
The wings had a normal-looking span for the size of the aircraft but were shorter front-to-back than seemed normal (to my very-much-not-expert eye)

Like the Islander it was a twin prop with a fairly pointy nose.
Does anyone have any idea what it was?

Could it be a Short Skyvan?

Or possibly a Short Sherpa?

@Monolo: Thanks. It looked a lot like that, but there was a distinct tail boom, rather than the body extending back to the tailplane.

@fooot: Thanks. More similar to the Skyvan, I'd've said, but see the note above to Monolo.

This list contains all aircraft which UK military is using. Can you spot yours in there?

@Farhan: Sadly, no. Thanks for the link. We do get historic craft flown around here periodically, so it may be something that used to be used...

There are US airbases in the UK as well.

What about a Flying Boxcar? http://en.wikipedia.org/wiki/Fairchild_C-119_Flying_Boxcar

@GdD: Thanks! But much smaller than that, with just the one tailboom.

I'm thinking I may just delete this. It's one thing to say "What's this aircraft" and produce a picture of the one in question, but a picture of one vaguely like it and a description of the differences may be a bit too much of an ask. :-) I do really appreciate everyone's attempts to find it, though!!

@T.J.Crowder - I think it's a good question. Certainly well detailed with more information than some other ID questions on here

@T.J.Crowder Can you provide the image source for the picture in your question?

@SentryRaven: I don't recall where I got it. I'll remove it.

It sounds an awful lot like a C-145, or maybe the 'civilian' version (it's primarily used by militaries), the  PZL Skytruck.
Source
It's used by the U.S. Air Force, so seeing it in Britain would not be surprising - all 3 of the U.S. Air Force's RAF joint use bases are within 100 air miles.

It's twin-engine, with a tailplane and twin fins
Its tail boom does narrow somewhat and distinguish itself, as seen here
It does have somewhat of a chunky body
The wings are fairly thin (front-to-back)

That has to be it, thank you! Goes to prove what memory is like (and seeing something only in glances -- I was driving on the motorway, after all). I could have sworn the tailboom was more distinct from the body, but looking at the pictures, this is the plane.

@SSumner Can you provide the image source for the picture in your answer?

@sentryraven - done